1. Field of the Invention
The present invention relates to a soft composite sheet and a method of producing it.
Many attempts have been made to obtain soft and dense artificial leather like that of natural leather.
Conventionally, these products comprise a base fiber structure and a binder. Attempts to improve the base fiber structure include the use of non-woven sheet, woven sheet, knitted sheet, and woven or knitted sheet integrated with short fiber web. On the other hand, super-fine fibers have been used as fibers which constitute base fiber sheet. Also the choice of binder for the synthetic leather, such as polyurethane, has been improved. But it has been extremely difficult to increase softness and drapability without significantly decreasing strength and abrasion resistance.
2. Description of the Prior Art
For example, U.S. Pat. No. 3,544,357 discloses softening methods involving adding a softening agent or a blowing agent to a binder prior to impregnation. Japanese Patent Publication No. 45502/83 (Tokko-sho No. 58-45502) discloses softening methods involving adding lubricant or releasing agent to a fiber base prior to impregnation with a binder, Japanese Patent Publication No. 9315/66 discloses softening methods involving removing one component of a multi-core type composite fiber which constitute a fiber base after binder impregnation. Further, softening methods involving mechanical crumpling are also known. However, these improvement are not satisfactory because a large amount of binder is necessary to keep strength and dimensional stability and the binder causes the artificial leather to exhibit stiffness and rubber-like elasticity. Furthermore, recent fashion trend necessitate more soft, thinner and lighter fabric (even softer than natural leather).
Hitherto applications of the high speed fluid jet treatment to fibrous sheets have been tried. They are: a method for entangling non-woven fabric (U.S. Pat. No. 4,476,186), a method for making an integrated sheet in which textile is interlocked with short fiber (U.S. Pat. Nos. 4,368,227, 4,145,468, 4,146,663). However, these methods are not methods for treating a sheet to which a binder has been applied.